EMP sensitivity and protection against EMP


#1

Most devices include their ESD voltage and ESD & EMI Protection schemes are described by IC vendors.

How do I calculate EMP sensitivity? Naturally any devices attached to antennas are most sensitive.

I guess my question is how to calculate an antennas’ full spectrum EMF coupling. That with an estimate of the power required to destroy electronics though its antennas would provided an estimate of the devices EMP sensitivity.

Am I thinking about this correctly. And means of calculate an antennas’ full spectrum EMF coupling are appreciated.


#2

ESD is a type of EMP.
An EMP is a Pulsed type of EMI.

And I think your question relates to Electromagnetic Compatibility system characteristics which is such a huge subject that it’s most often managed rather than predicted (calculated).

As the frequency components (due to their pulsed nature, EMPs are broadband) are unknown at design time, you would have to assume the EMP contains DC to “daylight” frequency components. This means that an antenna’s coupling would be irrelevant to the antenna’s frequency characteristics and it’s more directly related to the amplitude of the EMP.

I think basically you need to include sufficient EMI protection schemes to make sure any energy that makes it past ( shield, filters, transient absorbers, fuses, breakers ) are well below the component’s operational limits.


#3

Hi Tim,
(1) EMP susceptibility (Agricultural Automotive Equipment standard):
Critical Functions upto Electric Field Strength of 100V/m may not cause critical failures and below 30 V/m no failures allowed (not even non-critical failures).
A certified lab can advise you on the exact standard required.

(2) ESD: Use Human Body model
Any Accessible I/Os should withstand upto 8 kV while unpowered and 15 kV while powered up.

JEDEC standards can provide the tests as well.


#4

An antennas sensitivity depends on frequency, depending on its type and physical dimensions. So a long thin monopole will narrowly select one frequency, for example.
I guess it probably depends on what’s the anticipated source of noise/emp as well. So a highly directed parabolic could be expected to avoid an emp by looking the other way so to speak.


#5

Hi Tim,

To protect from ESD, you can do the following:
(1) Add Transient Voltage Suppressor (TVS);
(2) Use JFET ICs/Transistors instead of MOSFETS at I/O (similar to Multimeters, Oscilloscopes I/Os), e.g. JFET input op amps: LF356/357;
(3) Add RC filters at human accessible inputs, this will make the response slower.

Best,
RK